Angiogenesis refers to the process by which new capillary blood vessels are formed from existing microvessels, resulting in the development of a blood supply to a given area of tissue [23, 25]. It is one of the most pervasive and fundamentally essential biological processes encountered in mammalian organizations. In the healthy, adult human body, angiogenesis is a normal and important function that is critical in a variety of physiological settings, including chronic inflammation, embryonic development, reproduction, and wound healing [22, 29]. For example, angiogenesis occurs in the female reproductive system, in response to ovulation or gestation, and in the normal hair cycle [28]. Nevertheless, apart from the processes of wound healing and inflammation, angiogenesis virtually never occurs physiologically in adult tissues, except in the ovary, the endometrium, and the placenta [27].
When defective or uncontrolled, however, angiogenesis is also central to a number of pathological processes, including: abnormalities of wound healing in diseases such as diabetes and duodenal ulceration; chronic inflammatory disorders, such as rheumatoid arthritis, psoriasis, and periodontitis; dermatological conditions such as cutaneous malignancy, decubitus ulcers, hemangiomas, Kaposi""s sarcoma, psoriasis, pyogenic granulomas, and warts; diseases of the eye, particularly diabetic retinopathy; and growth of solid tumors, both benign and malignant [22, 23, 25, 26]. The consequence of abnormal angiogenesis is either excessive or insufficient blood vessel growth. Ulcers, strokes, and heart attacks, for example, can result from the absence of angiogenesis normally required for natural healing, while excessive blood vessel proliferation may favor arthritis, blindness, and tumor growth and dissemination [29 ].
The angiogenic process is tightly regulatedxe2x80x94in both time and spacexe2x80x94by a variety of endogenous angiogenic and angiostatic factors. It is propelled by a mixture of growth factors and pro-angiogenic cytokines, and is moderated by a collection of inhibitors of neovascularization which interfere with steps in the angiogenic process [22, 30]. In angiogenesis, capillary sprouts are formed in response to pro-angiogenic factors. The sprouts then grow and develop, driven by endothelial cell migration and proliferation, and organize themselves into a ordendritic structure [24]. Angiogenic and anti-angiogenic molecules control the formation of new vessels via different mechanisms. Hypoxia and other ill-defined stimuli drive tumor, inflammatory, and connective tissue cells to generate angiogenic molecules, such as vascular endothelial growth factor, fibroblast growth factor, transforming growth factor beta, and platelet-derived growth factor. Natural and synthetic angiogenesis inhibitors, such as angiostatin, thalidomide, and thrombospondin, can repress angiogenesis [23]. Most, if not all, of the angiogenesis-dependent disease processes result from both the unrestricted production of normal or aberrant forms of pro-angiogenic mediators, and the relative deficiency in angiogenic-inhibitory molecules [22].
Processes which are necessary for new vessel formation, and which are regulated by angiogenic and anti-angiogenic molecules, include the migration and proliferation of endothelial cells from the microvasculature, the controlled expression of proteolytic enzymes, the breakdown and reassembly of extracellular matrix, and the morphogenic process of endothelial tube formation. In animal models, some angiogenesis-dependent diseases can be controlled or modulated via induction or inhibition of new vessel formation [23]. The manipulation of new vessel formation, particularly the therapeutic induction of angiogenesis, would be desirable, as it would present new therapeutic options for treating a vast array of angiogenesis-dependent diseases or conditions, including cancer, diabetic retinopathy, inflammatory diseases, ischemic heart disease, myocardial infarction, peripheral vascular disease, and wound healing.
Onchocerciasis, or River Blindness, occurs primarily as a result of a host inflammatory response to infection with the filarial nematode Onchocerca volvulus (O volvulus). Transmitted by the bites of blackflies from the family Simuliidae, which breed in swiftly flowing streams, the parasite invades the skin, subcutaneous tissues, and other tissues, producing fibrous nodules. The host inflammatory response to infection with O volvulus may manifest in chronic skin disease and eye lesions. In the cornea, for example, this response produces neovascularizationxe2x80x94the seminal event in the pathologic response processxe2x80x94followed by corneal opacification. Ocular onchocerciasis is characterized by lesions of the anterior eye, including punctate keratitis, deformation of the pupil, and an ingrowth of fibrovascular scar tissue that may result in blindness. In fact, onchocerciasis is the second leading cause of infectious blindness in the world. Of the 18 million people who are believed to be infected with onchocerciasis, approximately 270,000 are blind, and a further 500,000 are visually impaired [1-4, 31].
A library of expressed sequence tags of O. volvulus has recently been developed by the Filarial Genome Project, and numerous cDNAs have been cloned [5]. From this library, a number of O. volvulus proteins, including Ov20 [32], OvPDI [11], and Ovzf [33], have been characterized. However, the relationship between proteins of O. volvulus and the host inflammatory response in ocular onchocerciasisxe2x80x94particularly in the induction of corneal neovascularizationxe2x80x94has not been fully delineated.
The present invention is based on the discovery that certain members of the Ov-ASP protein family are involved in the pathologic process of corneal neovascularization in animals infected with O. volvulus. This discovery, which indicates a pro-angiogenic role for Ov-ASP proteins, will have implications for wound healing and for the treatment of diseases, such as ischemia, where the enhancement or promotion of angiogenesis is desirable. In addition, this discovery permits screening for anti-Ov-ASP factors which inhibit or reduce the angiogenic activity of Ov-ASP. This finding will have implications in the treatment of ocular onchocerciasis.
Accordingly, the present invention provides a method for inducing angiogenesis in a tissue by contacting the tissue with an amount of Ov-ASP effective to induce angiogenesis in the tissue. The present invention further provides a method for screening for an anti-Ov-ASP factor, by contacting a factor of interest with Ov-ASP, and then assessing the ability of the factor to inhibit angiogenic activity of Ov-ASP. Finally, the present invention provides a method for inhibiting angiogenesis in a subject.